"—" means "the parameter of the type constructor goes here". I believe in Scala you use underscore for this, at the value level at least. "×" is what mathemat

"—" means "the parameter of the type constructor goes here". I believe in Scala you use underscore for this, at the value level at least. "×" is what mathematicians call the type constructor for the usual product type. In Haskell this is called (,). I don't know what it's called in Scala. So, — × M means something like "type T a = T a M", in Haskell notation.